<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function calculate(method, ...nums){
            let result;
            if(!method || nums.length == 0){
                alert('请输入参数!');
                return;
            }
            if(method == '*'){
                result = 1;
                for (let i = 0; i < nums.length; i++){
                    result *= nums[i];
                }
            } else if(method == '+'){
                result = 0;
                for (let i = 0;i < nums.length; i++){
                    result += nums[i];
                }
            }
            alert(result);
        }
        calculate("+",1,2); //3
        calculate("+",1,2,3,4,5); //15
        calculate("*",1,2,3); //6
        calculate("*",1,2,3,4,5); //120
    </script>
</body>
</html>